An aircraft generally comprises multiple electric machines distributed throughout the aircraft for fulfilling a set of diverse tasks. Known for example are electric machines dedicated to starting up a propulsion turbine, to an air conditioning system for the cabin of the aircraft, or dedicated to the operation of the flight control surfaces of the aircraft. For these tasks, DC, asynchronous, or synchronous, triphase, hexaphase or more generally, polyphase electric machines are notably used. These electric machines consume electrical power available on the onboard network of the aircraft, and for example supplied by a generator linked to a turbine or supplied by an airport network while the aircraft is on the ground.
It is known that it is essential to have reliable information on the position of the rotor of the electric machine. Any measurement error regarding the position significantly increases electrical losses. Typically, an error of less than 5% in the actual position is generally sought, the impacts on the machine being considered to be acceptable (an adverse effect on mass linked to machine oversizing, additional costs, notably for cooling, etc. . . . ). The electric machines implemented on board an aircraft exhibit high rotational speeds, of the order of 10,000 to 50,000 rpm, making it necessary to have information on the position of the high-frequency rotor, typically of the order of 8 to 40 kHz. Many techniques exist for evaluating the position of the rotor. A variety of sensors are known ensuring a physical measurement of the position, calculating means also exist allowing this position to be evaluated as a function of the voltages and currents measured in each of the phases of the machine.
In a conventional electrical architecture of an aircraft, each electric machine possesses one or more inverters linked to the onboard network which shapes the signal supplying power to each of the phases in accordance with the requirements of the machine. When the electric machine is not equipped with position sensors, a widespread conventional method implements a position estimator such as a Kalman filter. This estimator is based on phase currents flowing in the machine as well as phase-neutral voltages applied to the machine. FIG. 1 illustrates the principle of this position estimator in the case of an electric machine 11, supplied with power by a sole inverter 10. The three phase currents (in this case a triphase machine) are denoted by ia, ib, ic; the three phase-neutral voltages are denoted by Va, Vb, Vc. The three objects denoted by A correspond to three sensors respectively measuring the currents ia, ib, ic. The voltage VDC is the input voltage of the inverter, or DC bus voltage at the input of the inverter.
By measuring the currents and voltages, the estimator allows the rotor position θ0 and the rotor rotational speed ω0 of the electric machine to be determined using a function of the type:(θ0,ω0)=f(ia,ib,ic,Va,Vb,Vc)
Various known functions exist, using a Kalman filter or other techniques, allowing this estimation of position and speed. These known techniques are not covered again here in detail.
At this stage it is appropriate to mention that the present document only makes reference to phase currents and phase-neutral voltages, but that these generic designations refer more broadly:                for phase-neutral voltages:                    to phase-phase voltages,            to Park transformation vd-vq voltages,            to PWM Da, Db, Dc duty cycles,            to PWM duty cycles after Dq-Dd Park transformation,            or using any other transformation equivalent to a change of reference frame (for example Concordia)                        for phase currents, to Park transformation id-iq currents, or using any other transformation equivalent to a change of reference frame, for example Concordia.        
FIGS. 2a and 2b illustrate the principle of the estimation of position in the case in which an electric machine is supplied with power by multiple inverters, for example a number N of inverters. In a first known architecture, the inverters are connected in parallel by generally adding an inductance at the output of each bridge leg of the inverters, or the inverters can be coupled by a coupling inductor as shown in FIG. 2a. As previously, ia, ib, ic, Va, Vb and Vc represent the phase currents and the phase-neutral voltages of the machine. The phase currents and the phase voltages at the output of one of the N inverters, denoted by k, are denoted respectively by ika, ikb, ikc, Vka, Vkb and Vkc.
The connection of the inverters in parallel leads, for the phase currents, to:
      ia    =                  ∑                  k          =          1                n            ⁢      ika        ,      ib    =                  ∑                  k          =          1                N            ⁢      ikb        ,      ic    =                  ∑                  k          =          1                N            ⁢      ikc      which can be generally expressed as:
      iabc    =                  ∑                  k          =          1                N            ⁢      ikabc        ;and for the phase-neutral voltages, it can be shown that:
      Va    =                  (                              ∑                          k              =              1                        N                    ⁢          Vka                )            /      N        ,      Vb    =                  (                              ∑                          k              =              1                        N                    ⁢          Vkb                )            /      N        ,      Vc    =                  (                              ∑                          k              =              1                        N                    ⁢          Vkc                )            /      N      which can be generally expressed as:
  Vabc  =            (                        ∑                      k            =            1                    N                ⁢        Vkabc            )        /          N      .      
In a second known architecture shown in FIG. 2b, the machine comprises multiple sub-machines, each one being supplied with power by a dedicated inverter. The phase currents and phase-neutral voltages of the N inverters are denoted as in the parallel architecture described previously, and as shown in FIG. 2b. 
In a known manner, a machine comprising N sub-machines can be modeled by simple machine; the phase currents and phase-neutral voltages then being respectively determined by the following relationships:
                              iabc          =                                    ∑                              k                =                1                            N                        ⁢            ikabc                          ,                              and            ⁢                                                  ⁢            Vabc                    =                                    (                                                ∑                                      k                    =                    1                                    N                                ⁢                Vkabc                            )                        /                          N              .                                                          (        i        )            
Both architectures therefore result in the same equations, the equations (i) above. To determine the rotor position of the machine, the position estimator previously described therefore needs to know either:
The phase currents and the phase-neutral voltages at the input of the machine, i.e. ia, ib, Va, Vb and Vc, and the rotor position is then calculated by a relationship of the type:(θ0,ω0)=f(ia,ib,ic,Va,Vb,Vc)
The phase currents and the phase-neutral voltages at the output of each of the N inverters, and the rotor position is then calculated by a relationship of the type:(θ0,ω0)=f(ia,ib,ic,Va,Vb,Vc)in which ia, ib, ic, et Va, Vb, Vc are defined by the equations (i) reproduced below:
      iabc    =                  ∑                  k          =          1                N            ⁢      ikabc        ,            and      ⁢                          ⁢      Vabc        =                  (                              ∑                          k              =              1                        N                    ⁢          Vkabc                )            /              N        .            
In the known solutions, a shared control member generates the phase currents and the phase-neutral voltages for each of the N inverters. In practice, the control member is the element which performs the regulation of current and the generation of duty cycles. It takes the form, for example, of a circuit board with one or more components of the type microcontroller, microprocessor or more simply, programmable logic circuit. The control member has access to the phase current measurements ia, ib, ic, used for the regulation of current, and to the phase-neutral voltages Va, Vb, Vc, which are deduced from the duty cycles and from the input voltage of the inverter or possibly from voltage sensors at the output of the inverter.
In the known solutions, the control member shared by the N inverters therefore has all the information required for estimating the position. However, this architecture has limits which the present invention seeks to overcome. It actually involves a fixed assignment of the N inverters to the electric machine. The inverter/inverters dedicated, for example, to an electric machine charged with starting up the turbine is only used when the aircraft is on the ground before takeoff. In flight, the unused inverter represents an unwanted mass and unwanted cost. Similarly, a failure of an inverter renders an otherwise operational electric machine unusable. For these reasons, it is desirable to have a more modular electrical architecture, which would allow the assignment of one or more inverters to be modified between multiple electric machines. Following the flight phase of the aircraft, or a particular event such as the breakdown of an inverter, a new assignment of the inverters could be considered.
A modular power bay controlling the power supply of a set of electric machines distributed throughout the aircraft by means of a set of inverters is envisaged. The implementation of such a modular bay encounters, in the case of electric machines without position sensors, difficulties in estimating the position of each one of the electric machines by means of phase currents and phase-neutral voltages, to the extent that the architecture of the inverters charged with shaping the power supply signal of the machine is variable. On the one hand, the position information must be available at the level of each inverter, at high frequency for the phase current regulations; on the other hand, the position estimator must be able to adapt simply to a reassignment of the inverters.